This invention relates to a check valve and more particularly to a pressure responsive check valve which is opened for controlled reverse fluid flow therethrough when the fluid pressure at the blocked side exceeds a preselected pressure level.
Various embodiments of dual source fluid supply systems for hydraulic circuits have been utilized which have two sources or pumps delivering fluid under pressure to a steering circuit. In one embodiment of these systems, the respective pumps are operatively associated with main relief valves which relieve excessive fluid pressure developed by the pumps. Also operatively associated with the pumps are a pair of check valves which prevent cross flow between the pumps in the event that one of the pumps should become nonoperative. Although the control valve of FIG. 2 is a closed center valve, there is limited or restricted fluid flow through orifices in the valve when the valve is in the position shown. Such orifices are disclosed in FIG. 2 of the drawings of the present application.
One of the problems encountered in such a system is that the check valves are positioned between the steering cylinders and the relief valves and block reverse flow from the steering cylinders to the pump and relief valve. Thus, upon a sharp pressure build-up in a steering cylinder due to, for example, a wheel of the vehicle striking an object, such pressure is not relieved to any great extent since the check valve prevents reverse flow from the steering cylinders to the relief valve. In extreme cases, the pressure buildup can cause damage to the pins and brackets which connect the steering cylinders to the vehicle.